1. Field of the Invention
The present invention relates to a method utilized in a wireless communication and communication device thereof, and more particularly, to a method for improving transmission of packet elements in a wireless communication system and communication device thereof.
2. Description of the Prior Art
As today's applications for electronic systems grow at ever-increasing rates, the demand for better communications performance is never ceasing. Standards for various technologies such as the 3rd Generation Partnership Project (3GPP) High-Speed Packet Access (HSPA) and Long Term Evolution (LTE) work towards creating more efficient communication systems.
Architecture of the radio interface protocol of a LTE system includes three layers: the Physical Layer (Layer 1), the Data Link Layer (Layer 2), and the Network Layer (Layer 3), where a control plane of Layer 3 is a Radio Resource Control (RRC) layer, and Layer 2 is further divided into a Packet Data Convergence Protocol (PDCP) layer, a Radio Link Control (RLC) layer and a Medium Access Control (MAC) layer.
The main services and functions of the MAC layer include mapping between logical channels and transport channels; multiplexing/demultiplexing of RLC PDUs (protocol data units) belonging to one or different radio bearers into/from transport blocks (TB) delivered to/from the physical layer on transport channels; buffer status reporting; power headroom reporting; error correction through HARQ; priority handling between logical channels of one UE; priority handling between UEs by means of dynamic scheduling; and padding.
A MAC PDU consists of a MAC header, zero or more MAC Service Data Units (SDUs), zero, or more MAC control elements, and optional padding. Both the MAC header and the MAC SDUs are of variable sizes. A MAC PDU header consists of one or more MAC PDU sub-headers; each subheader corresponding to either a MAC SDU, a MAC control element or padding. MAC PDU sub-headers have the same order as the corresponding MAC SDUs, MAC control elements and padding.
MAC control elements transmitted by a UE include a buffer status report (BSR) MAC control element, a power headroom report (PHR) MAC control element and C-RNTI (cell radio network temporary identifier) MAC control element. The Buffer Status reporting procedure is used to provide the serving eNB with information about the amount of data in the UL buffers of a UE for scheduling of uplink transmission. A Buffer Status Report MAC control element consists of either a short BSR and truncated BSR format or long BSR format.
If a BSR has been triggered since the last transmission of a BSR or this is the first time that a BSR is triggered and the UE has UL resources allocated for new transmission for this TTI, the UE generates a BSR MAC control element. However, the allocated UL resources may have insufficient capacity to transmit the generated BSR MAC control element. In this situation, the BSR is delayed.
Issue 1 is described as follows. When a BSR has been triggered since the last transmission of a BSR or this is the first time that a BSR is triggered and the UE has UL resources (e.g. transport blocks) allocated for new transmission for this TTI, the UE instructs a Multiplexing and Assembly procedure to generate a BSR MAC control element and starts/restarts the PERIODIC BSR TIMER. However, some transport block sizes (e.g. 16 and 24 bits) cannot include a long BSR (32 bits) if a long BSR is triggered. Besides, at serving cell change, the first UL-DCCH (Uplink Dedicated Control Channel) MAC SDU to be transmitted in the new cell has higher priority than MAC control elements for BSR. It is possible that the remaining space of the transport block which has included a C-RNTI and the first UL-DCCH MAC SDU is insufficient for a long BSR (32 bits) or a short BSR (16 bits). In this situation, the BSR MAC control element is still generated but unable to be transmitted in the TTI due to insufficient space of the transport block. One drawback is that the system failure occurs in an implementation. Another drawback is that the BSR is delayed to be sent to the eNode B. This impacts the scheduling efficiency of the eNode.
The Power Headroom reporting procedure is used to provide the serving eNB with information about the difference between the UE TX (Transmission) power and the maximum UE TX power. If a PHR has been triggered since the last transmission of a PHR and the UE has UL resources allocated for new transmission for this TTI, the UE obtains the value of the power headroom from the physical layer, and generates a PHR MAC control element based on the value reported by the physical layer. However, the allocated UL resources may have insufficient capacity to transmit the generated PHR MAC control element. In this situation, the PHR is delayed.
Issue 2 is described as follows. When a PHR has been triggered since the last transmission of a PHR and the UE has UL resources allocated for new transmission for this TTI, the UE obtains the value of the power headroom from the physical layer, instructs the Multiplexing and Assembly procedure to generate a PHR MAC control element based on the value reported by the physical layer. If the PHR is a “Periodic PHR”, the UE restarts the PERIODIC PHR TIMER, and the UE restarts the PROHIBIT_PHR_TIMER. However, Issue 2 has similar problems to issue 1. Some transport block sizes (e.g. 32, or 40 bits) including a long BSR (32 bits) cannot include a PHR (16 bits), or some transport block sizes (16 or 24 bits) including a short BSR cannot include a PHR (16 bits). Besides, at serving cell change, the first UL-DCCH MAC SDU to be transmitted in the new cell has higher priority than MAC control elements for BSR. It is possible that remaining space of the transport block including a C-RNTI, the first UL-DCCH MAC SDU, and a BSR cannot include a PHR (16 bits). In this situation, the PHR MAC control element is still generated but unable to be transmitted in the TTI due to insufficient space of the transport block. One drawback is that the system failure occurs in an implementation. Another drawback is that a PHR is delayed to be sent to an eNode B. This impacts the scheduling efficiency of the eNode.
Issue 3 is described as follows. The range of the transport block size containing one MAC PDU is from 16 to 149776 bits with 24 bit CRC (cyclic redundancy check) error detection. A residual (undetected) error rate of the received MAC PDU is higher for a larger transport block size. A High residual error rate degrades the system performance.